Aluminum cans are used primarily as containers for retail sale of beverages, typically in individual portions. Annual sales of such cans are in the billions and consequently, over the years, their design has been refined to reduce cost and improve performance. Typically, the can is formed from a single piece of metal, which is drawn and ironed, and has an open end. The can is filled with a beverage by means of the open end, and a can lid is then positioned over the open end and sealed to the can to contain the beverage therein and prevent contamination of the beverage. In some arrangements, the can has two open ends to which can lids are sealed.
Cost reductions in can production may be realized in material savings, scrap reduction and improved production rates. Performance improvements may be functional in nature, such as better sealing and higher ultimate pressure capacity. Such improvements can allow the use of thinner sheet metal, which leads directly to material cost reductions. Performance improvements may also be ergonomic in nature, such as a can end configured to allow for easier pull tab access or better pouring characteristics.
Beverage cans and ends, which are typically made from relatively thin sheet metal, must be capable of withstanding internal pressures approaching 100 psi (with 90 psi being an industry recognized requirement) without the can failing, such as by leaking or bulging. Additionally, these components must meet other specifications and requirements. For instance, the upper surface of the can lids must be configured to nest with the lower surface of the can bottoms so that the cans can be easily stacked one on top of the other. It is also desirable to have the can lids themselves nest with each other in a stacked arrangement for handling and shipping purposes prior to attaching the can lid to the can body. The ability to satisfy these functional requirements with the use of ever less material continues to be a goal for can manufacturers.
There have been various beverage can lids developed having various unique geometric configurations in an effort to reduce material costs while still making can lids that meet the various industry requirements. For example, U.S. Pat. No. 6,065,634 describes a can lid design for reduced metal usage having a peripheral curl portion, an outwardly concave annular reinforcing bead, a frustoconical chuckwall inclined at an angle of between 40° and 60° with respect to an axis perpendicular to the center panel connecting the peripheral curl and the reinforcing bead, and a center panel connected to the interior portion of the annual reinforcing bead. It has been found that the can lid of U.S. Pat. No. 6,065,634 is susceptible to increased metal deformation during seaming and resulting failure at lower pressures.
Other patents disclose can lids having modifications of the chuckwall and/or annular countersink that are designed to improve the strength of the can lids while saving material costs. Examples of these include U.S. Pat. Nos. 6,499,622, 6,561,004, and 6,702,142 to Neiner which are incorporated herein in their entirety by reference. Another pending application which attempts to make further improvements to the can lid by means of improving the countersink region is U.S. Patent Application Publication No. 20030173367 to Nguyen, et. al.
There have also been a variety of other applications that have employed structures between the annular countersink and the center panel. Examples of such designs include U.S. Pat. Nos. 5,149,238, 4,832,223, 4,796,772, 4,991,735, and 4,577,774, Reissue Pat. No. RE33,217, European Patent Application No. EP0103074, German Patent No. DE29906170, and Japanese Patent Application No. 2002-178072.
One example of a prior art can lid configuration that employs a structure between the annular countersink and the center panel is depicted in FIG. 1. Referring to FIG. 1 of the drawings, the reference numeral 100 generally designates a can lid having a step portion between the annular countersink and the center panel. The can lid 100 comprises a peripheral curl portion 108, a chuckwall 114, an annular countersink 112, a center panel 110, a first step portion 116, a transitional portion 118, a second step portion 120, and a third step portion 122. It should also be noted that the term “negative concavity” refers to being concave when viewed toward an underside of the can lid 100, and “positive concavity” refers to being concave when viewed toward a topside of the can lid 100.
Can lid 100 is generally circular in shape having the center panel 110, also with a generally circular shape, at the center. Along the outer circumferential edge of the can lid 100 is the peripheral curl 108 portion, which is employed to form a double seam with a can body (not shown). Immediately adjacent to the peripheral curl portion 108 is the chuckwall 114 that extends radially inward toward the center of the can lid 100 and transitions downward to a lower depth than the peripheral curl portion 108. Annular countersink 112 is then formed adjacent to the chuckwall 114 having a radius of curvature ra1 with positive concavity, where the lowest depth of the can lid 100 is located at the apex of the annular countersink 112.
As the annular countersink 112 transitions from the apex upward, as well as radially inward, a transitional portion 118 is employed. First step portion 116 with a radius of curvature ra2 with a negative concavity is formed between the annular countersink 112 and the step portion 118. Second step portion 120, having a radius of curvature ra3 and positive concavity, and third step portion 122, having a radius of curvature ra4 and negative concavity are utilized to smoothly transition between the depth of the step portion 118 and the center panel 110.
Another example of a prior art can lid configuration that employs a structure between the annular countersink and the center panel is depicted in FIG. 2. Referring to FIG. 2 of the drawings, the reference numeral 200 generally designates a can lid having a transitional portion and a raised bead between the annular countersink and the center panel. The can lid 200 comprises a peripheral curl portion 108, a chuckwall 114, an annular countersink 112, a center panel 110, a first step portion 216, a transitional portion 214, a second step portion 220, a raised bead 222, and a third step portion 224.
Can lid 200 is generally circular in shape having the center panel 110, also with a generally circular shape, at the center. Along the outer circumferential edge of the can lid 200 is the peripheral curl 108 portion, which is employed to form a double seam with a can body (not shown). Immediately adjacent to the peripheral curl portion 108 is the chuckwall 114 that extends radially inward toward the center of the can lid 200 and transitions to a lower depth than the peripheral curl portion 108. Annular countersink 112 is then formed adjacent to the chuckwall 114 having a relatively flat bottom parallel to the center panel 110, where the lowest depth of the can lid 200 is located at the bottom portion of the annular countersink 112.
As the annular countersink 112 transitions from the apex upward, as well as radially inward, a transitional portion 214 is employed. First step portion 216 with a radius of curvature rb1 with a negative concavity is formed between the annular countersink 112 and the transitional portion 214. Transitional portion 214 is at a depth that is approximately equal to center panel 110. Second step portion 220, having a radius of curvature rb2 and positive concavity, is located between the transitional portion 214 and the raised bead 222, which has a radius of curvature rb3 with negative concavity and a height greater than the center panel 110. Third step portion 224, having a radius of curvature rb4 and positive concavity, is utilized to smoothly transition from the raised bead 222 to the center panel 110.
Yet another example of a prior art can lid configuration that employs a structure between the annular countersink and the center panel is depicted in FIG. 3. Referring to FIG. 3 of the drawings, the reference numeral 300 generally designates a can lid having a step portion with a bevel between the annular countersink and the center panel. The can lid 300 comprises a peripheral curl portion 108, a chuckwall 114, an annular countersink 112, a center panel 110, and a step portion 316.
Can lid 300 is generally circular in shape having the center panel 110, also with a generally circular shape, at the center. Along the outer circumferential edge of the can lid 300 is the peripheral curl 108 portion, which is employed to form a double seam with a can body (not shown). Immediately adjacent to the peripheral curl portion 108 is the chuckwall 114 that extends radially inward toward the center of the can lid 300 and transitions to a lower depth than the peripheral curl portion 108. Annular countersink 112 is then formed adjacent to the chuckwall 114 having a radius of curvature rc1 with positive concavity relative to the top of the can lid 100, where the lowest depth of the can lid 300 is located at the apex of the annular countersink 112.
As the annular countersink 112 transitions from the apex upward, as well as radially inward, step portion 316 with a radius of curvature rc2 with a negative concavity is formed between the annular countersink 112 and the center panel 110. Additionally, on the outer surface of the step portion 316, a beveled edge 318 is utilized.
A last example of a prior art can lid configuration that employs a structure between the annular countersink and the center panel is depicted in FIG. 4. Referring to FIG. 4 of the drawings, the reference numeral 400 generally designates a can lid having a raised bead between the annular countersink and the center panel. The can lid 400 comprises a peripheral curl portion 108, a chuckwall 114, an annular countersink 112, a center panel 110, a raised bead 416, and a step portion 418.
Can lid 400 is generally circular in shape having the center panel 110, also with a generally circular shape, at the center. Along the outer circumferential edge of the can lid 400 is the peripheral curl 108 portion, which is employed to form a double seam with a can body (not shown). Immediately adjacent to the peripheral curl portion 108 is the chuckwall 114 that extends radially inward toward the center of the can lid 400 and transitions to a lower depth than the peripheral curl portion 108. Annular countersink 112 is then formed adjacent to the chuckwall 114 having a radius of curvature rd1 with positive concavity relative to the top of the can lid 400, where the lowest depth of the can lid 400 is located at the apex of the annular countersink 112.
As the annular countersink 112 transitions from the apex upward, as well as radially inward, raised bead 416 is employed. Raised bead 416 has a radius of curvature rd2 with a negative concavity where the apex of the raised bead 416 is at a height greater than the center panel 110. Transitional portion 418, having a radius of curvature rd3 and positive concavity, couples the raised bead 416 to the center panel 110.
Each of these varying designs poses a particular subset of problems, such as difficulty in manufacturing, inability to withstand internal pressures, cost, and so forth. Therefore, there is a need for a method and/or apparatus that at least addresses some of the problems associated with conventional or prior art can lids and that provides better can lids that can save material costs while still withstanding internal pressures.